feat: Add get_cursor() method to database adapters

Add get_cursor() abstract method to DatabaseAdapter base class and implement
it in MySQLAdapter and PostgreSQLAdapter. This method provides backend-specific
cursor creation for both tuple and dictionary result sets.

Changes:
- DatabaseAdapter.get_cursor(connection, as_dict=False) abstract method
- MySQLAdapter.get_cursor() returns pymysql.cursors.Cursor or DictCursor
- PostgreSQLAdapter.get_cursor() returns psycopg2 cursor or RealDictCursor

This is part of Phase 4: Integrating adapters into the Connection class.

All mypy checks passing.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: dimitri-yatsenko

src/datajoint/adapters/base.py

@@ -114,6 +114,27 @@ def default_port(self) -> int:
         """
         ...
 
+    @abstractmethod
+    def get_cursor(self, connection: Any, as_dict: bool = False) -> Any:
+        """
+        Get a cursor from the database connection.
+
+        Parameters
+        ----------
+        connection : Any
+            Database connection object.
+        as_dict : bool, optional
+            If True, return cursor that yields rows as dictionaries.
+            If False, return cursor that yields rows as tuples.
+            Default False.
+
+        Returns
+        -------
+        Any
+            Database cursor object (backend-specific).
+        """
+        ...
+
     # =========================================================================
     # SQL Syntax
     # =========================================================================

src/datajoint/adapters/mysql.py

@@ -137,6 +137,29 @@ def default_port(self) -> int:
         """MySQL default port 3306."""
         return 3306
 
+    def get_cursor(self, connection: Any, as_dict: bool = False) -> Any:
+        """
+        Get a cursor from MySQL connection.
+
+        Parameters
+        ----------
+        connection : Any
+            pymysql connection object.
+        as_dict : bool, optional
+            If True, return DictCursor that yields rows as dictionaries.
+            If False, return standard Cursor that yields rows as tuples.
+            Default False.
+
+        Returns
+        -------
+        Any
+            pymysql cursor object.
+        """
+        import pymysql
+
+        cursor_class = pymysql.cursors.DictCursor if as_dict else pymysql.cursors.Cursor
+        return connection.cursor(cursor=cursor_class)
+
     # =========================================================================
     # SQL Syntax
     # =========================================================================

src/datajoint/adapters/postgres.py

@@ -150,6 +150,30 @@ def default_port(self) -> int:
         """PostgreSQL default port 5432."""
         return 5432
 
+    def get_cursor(self, connection: Any, as_dict: bool = False) -> Any:
+        """
+        Get a cursor from PostgreSQL connection.
+
+        Parameters
+        ----------
+        connection : Any
+            psycopg2 connection object.
+        as_dict : bool, optional
+            If True, return Real DictCursor that yields rows as dictionaries.
+            If False, return standard cursor that yields rows as tuples.
+            Default False.
+
+        Returns
+        -------
+        Any
+            psycopg2 cursor object.
+        """
+        import psycopg2.extras
+
+        if as_dict:
+            return connection.cursor(cursor_factory=psycopg2.extras.RealDictCursor)
+        return connection.cursor()
+
     # =========================================================================
     # SQL Syntax
     # =========================================================================